This Carthusian monastery complex was founded in 1325, although its present appearance is the result of much 16th-century reworking. Renowned for its priceless architectural and artistic assets, San Martino was dissolved under French rule (1806-15); the monks returned only briefly before the certosa (charterhouse) was wrested from them again in the wake of Italian Unification in 1861. State of the art visitor facilities, airy rooms and terraced gardens with sweeping views over the Naples waterfront make the Certosa one of the city's must-sees.

The church's late 17th-century façade, opposite the ticket barrier, is by Cosimo Fanzago; it conceals remnants of the Gothic original, such as the pointed arches and cross-vaulted ceiling in the pronaos (projecting vestibule), which has 17th-century frescoes by Micco Spadaro depicting the persecution of Carthusians in England during Henry VIII's reign.

The church's interior contains as complete an array of Neapolitan art as you could hope for. Massimo Stanzione's Deposition (1638) dominates the inner façade, flanked by two fine portraits by Giuseppe Ribera, who is also responsible for the 12 paintings of prophets (1638-43) tucked into the spandrels of the arches. The delicate 18th-century marble altar balustrade is by Giuseppe Sammartino. The walls and side chapels feature paintings by the Vaccaros, Francesco Solimena and Stanzione. In the vaulted ceiling are frescoes (1637-40) by Giovanni Lanfranco: Ascension with Angels, Apostles and Saints. Bonaventura Presti used material already prepared by Fanzago for his intricate inlaid marble floor (1664).

The choir features Ribera's Communion of the Apostles, Guido Reni's Adoration of the Shepherds (1642), and Battista Caracciolo's Washing of Feet (1622), and the sacristy has some exquisite marquetry; on the cupboards, 56 panels depict biblical scenes. In the Cappella del Tesoro are Ribera's Pietà and frescoes by Luca Giordano; the parlatorio and chapter room (where there are several works by Battista Caracciolo) are also essential viewing.

A long passageway leads left out of the small chiostro dei procuratori into the chiostro grande (great cloister) - one of Italy's finest. This bright, sunny area was created in the 16th century by Giovanni Antonio Dosio; Cosimo Fanzago added the small monks' graveyard (note the skulls) and the busts and statues above the pillared portico, as well as the grotesque faces animating the well.

The Museo dell'Opera art gallery is beautifully laid out around the main cloister. The majority of the 17th- and 18th-century works, originally created for the monastery, is now housed in the prior's quarters in the southern wing (rooms 17 to 23). The collection includes works by Ribera (Sts Jerome and Sebastian), Lanfranco (Our Lady of the Rosary) and Stanzione (Baptism of Christ); Spadaro created the ceilings in rooms 14, 15 and 16. Room 8 contains a remarkable sculpture, the Madonna and Child with the Infant John the Baptist, by Pietro Bernini (father of the more famous Gianlorenzo).

The certosa, the Carthusian order and the history of Naples are constant themes in the works. There are splendid maps and landscape paintings, ranging from the anonymous Tavola Strozzi, with its detailed depiction of 15th-century Naples in room 32, and Didier Barra's bird's-eye view of Naples at the end of the 16th century, to a fine series of late 17th-century paintings by Gaspar Van Wittel in room 40. On the first floor are 19th-century paintings by local artists.

Another section is devoted to Nativity scenes, including a massive presepe (crib) with rare 18th century pieces, named after its 19th-century creator, Cuciniello. It's a marvellous depiction of what life in Naples would have been like centuries ago, complete with lighting effects that simulate the diurnal cycle. You'll also find displays on theatre, shipping and, in the former pharmacy, glassware and porcelain.

Not all of the Certosa's treasures will be on display when you visit, due to the usual problems of understaffing and restoration. If you want to see a specific work, phone ahead.